Slotted cylindrical antenna systems



1957 N. E. LINDENBLAD 2,803,008

SLOTTED CYLINDRICAL ANTENNA SYSTEMS Filed Dec. 28, 1953 IN VE YTOR. NILSE. LINDENBI. am

By M746 g ATTORNEY United States Patent SLOTTED CYLINDRICAL ANTENNASYSTEMS Nils Erik Lindenblad, Princeton, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application December28, 1053,.Serial No. 400,472 19 @laims. (Cl. 343-770) The inventionrelates to slot antennas and particularly pertains to an ultrahighfrequency slotted cylinder antenna array.

Broadcasting of television program service in the ultrahigh frequencyband between 470 and 1000 megacycles/ second imposes severe requirementsfor the necessary antenna systems. Efiective radiated powers of 100 to200 kilowatts are necessary, and a power handling ability up to 1000kilowatts of effective radiated power is desirable. Antenna power gainsto obtain up to 200 kilowatts of eiiective radiated power must be of theorder of 20 to 30 times that of a simple tuned dipole to permit thesehigh values of elfective radiated power to be obtained with transmitterequipment of good efiiciency and nominal power output. The dimensions ofsuch a radiation system in the ultrahigh frequency bands are muchsmaller than for the lower frequencies so that there is less thansufiicient room for the prior art type of transmission line assemblies.

It is'an object of the invention to provide an improved ultrahighfrequency, omnidirectional, high power antenna system of simpleconstruction'for operation over a relatively wide frequency band.

It is another object to provide a slot antenna system having a simple,centrally-located balanced transmission line.

These and other objects of the invention which will appear as thespecification progresses are attained by means of a transmitting orreceiving antenna system comprising a hollow tubular conductive memberhaving a pinrality of elongated longitudinal slots arranged along thelength of the member in pairs or groups of slots spaced about theperiphery. Radio frequency energy is distributed to the plurality ofslots from an externally located transmitting transducer or collectedfrom the slots and delivered to a receiving transducer by a balancedtransmission l-ine comprising a pair of conductors spaced apart onopposite sides of the longitudinal of and located within the tubularconductive member. The. conductors are spaced from the interior'wallportions of the tubular conductive member so as to induce current flowtherein and are located at such angles with respect to the slots as toproperly polarize theedges of the slots for radiation or reception of.energy to and from ambient space.

In one basic embodiment of the. invention a pair of longitudinal slotsare located diametrically opposite each other in the wall, portions of aconductive cylinder and the conductorsof abalanced transmission line arelocated in a plane passing through the axis of the cylinder and normalto the plane passing through both slots. The opposing edges of the slotswill be at the same instantaneous polarity while the opposing edges ofeach slot. will be of opposite polarity to. effect a transfer of energybetween the conductors of the transmission line and' ambient space. 0

Another basic embodiment. of the invention comprises a cylinder havingfour such slots located at intervals of ninety'degrees about theperiphery of the cylinder- One. pair of transmission line conductors arelocated in the plane passing through one pair of diametrically opposedslots to energize the other pair of slots as herein before described.Another pair of transmission line conductors are similarly located inthe plane of the other slots to energize the first slots withoutinteraction between the other slots due to the same polarization ofapposing edges of the one pair of slots. 7 The conductors of thetransmission lines are arranged with the median planes intersecting atthe axis of the cylinder thereby to prevent interaction between thebalanced transmission line currents directly. The arrangements abovedescribed may be stacked one on top of the other provided the centers ofthe slots are spaced in the vertical direction substantially awavelength, or a multiple thereof, apart to insure proper phase relationship of the slots on-a'ny given side of the cylinder. Where adual-transmission line feed is used it is preferable to place the slotsenergized by one transmission line in a difierent level from that inwhich the slots excited by the other transmission line are located.

An alternateconstructionof the basic embodiment comprises a pair ofsemi-circular members arranged to form a tubular structure having a pairof continuously extending slots. The transmission line is transposedevery half wavelength in order to properly polarize the edges of theslots. This assembly isalso adaptable for four slots and twotransmission lines fed by staggering the transpositions of the twotransmission lines.

Either standing wave or travelling wave energy may be applied to thetransmission lines. If travelling waves are used, the transmissionlines'are terminated by impedance elements matching the transmission linecharacteristics or the energy may bereturned over a shieldedtransmission line preferably located at the axis of the cylinder.Standing wave'energy, however, is considered the more practical form forapplications.

In order that the invention may be more clearly understood and readilyput to practical use, circuit arrange ments embodying the invention arehereinafter described, by way of example only, with reference to theaccompanying drawing in which:

I Fig. l is an elevation view of an antenna system according to theinvention;

Fig. 2' is a cross-section view taken along the line 22', of a portionof the antennashown in Fig. 1 illustrating essential details ofanantenna system according to the invention; 7

Fig. 3 is a cross-sectionview of another alternate at rangement of theantenna of the invention;

Fig; 4 is an elevation viewof an alternate embodiment of an antennaaccording to the invention;

Fig. 5 is a cross-section view of still another alternate arrangement ofthe antenna of the invention;

Fig. 6 is an elevation view of another. embodiment of the antenna.according to the invention;

' Fig. 7 is a cross-section view of the antenna according to theinvention as shown in Fig. 6 taken along the line 7-7.

Fig. 8 is an" illustration of an alternative arrangement together withagraphical representation ofthe' field pattern obtained therewith. 4

Referring to Fig. 1, there is shown an elevation view of an antennasystem according to? the invention. The radiation transferring elementconsists of a cylinder 20, which in practice is usually a galvanizedsteel tube,.hav'- ing oppositely disposed longitudinally arrangedelongated apertures or slots22--2S therein. The term cylinder as usedherein is-considered to be the surface traced by any straight line,called generatrix or element, moving parallel toa fixed. straight line,according to- Websters New International unabridged dictionary, 1953edition; These slots as shown are approximately a" half wavelength longat'the operating frequency and are spaced a wavea length apart betweentheir centers. Variations of these dimensions will be apparent to thoseskilled in the art. For example, the thickness of the tube will providesome capacitive reactive loading, calling for a corresponding shorteningof the slots to compensate. In practice the slots are usually eitherfilled in or covered with an insulating material which also alfects thedimensioning.

The slots 2225 are preferably covered by polyethylene slot covers heldin place by end and side clamping fixtures. A convex construction ofslot covers is preferably employed to reduce the area of the slots inwhich high frequency currents flow. The use of the protruding slotcovers also prevents deleterious eflfects of certain wind velocities onthe tube 20 which may set up a harmonic vortex wave. v

A pair of elongated conductors 28 and-29, preferably tubular forpractical reasons, are arranged within thelcyk inder 20. Theseconductors are-of-such diameter and are spaced apart at a distance atwhich a balanced transmission line is elfected at the desired operatingfrequency. Further, according to the invention, the relationship of thediameter of the transmission line conductors 28, 29 to the innerdiameter of the cylinder 20 is such that energy present in thetransmission line is effective to induce a current flow at the operatingfrequency in the wall portions of the cylinder 20 and thus excite theslots 2225. A cross-section view of the antenna system is shown in Fig.2, wherein the balanced transmission conductors'28, 29 are located in aplane substantially at right angles to any plane passing through both ofthe slots 24, 25.

The conductive surface element formed by the wall portion 32 of thecylinder 20 lying between the slots 24, 25 and nearest one of theconductors 28 will have currents of given intensity and direction offlow orjpolarity opposite to the direction of flow or polarity ofcurrents of the same intensity in the other wall portion 33 induced bythe proximity of the other conductor 29. Thus the apposite edges of theslots 24 and 25 are of opposite instantaneous polarity as required forradiation.

In the interest of clarity and convenience the longitudinal edges ofeach pair of slots which lie diametrically opposite each other or whichappear in the same'relative position in a traverse about the peripheryin a single direction are hereinafter termed the corresponding edges,and the edges which are immediately opposite eachother are termed theopposing edges as against the apposing of the same slot. For example,edges 34 and 35 of the section shown in Fig. 2 are apposing edges, asare edges 36 and 37. Edges 35 and 36 which are diametrically oppositeeach other are corresponding edges, while opposing edges 35 and 37 areimmediately opposite each other. With respect to a given edge 34, theedge 35 of the same slot is the apposite edge; the immediately opposingedge 36 is the opposite edge, and the diametrically opposite edge 37 isthe corresponding edge.

' At the same time the opposing edges of the slots 24, 25 are at thesame instantaneous polarity, providing the advantages set forth in U. S.Patent 2,660,670 issued November 24, 1953 to Dr. George H. Brown. Thesecurrent conditions are afforded without any restrictions on thecircumferential dimensions of the cylinder 20.

offsetting of the slots 24, 25 with respect to the conductors 28, 29 canbe effected if the circumferential dimensions are chosen accordingly. Anexample of such an arrangement is shown in Fig. 3, wherein thecircumference of the cylindeer 20 is approximately one wavelength, atthe operating frequency. Each wall portion 32, 33 between two radiatingslots 24, 25 should be an electrical half wavelength, or an odd multiplethereof, at the operating frequency so that each end of each portionwill be of opposite instantaneous polarity with respect to the other enddue to the time for the current wave to travel the distance. In thisarrangement corresponding edges will be of the same polarity asdistinguished from the polarity relationship of the arrangement of Fig.2.

no interaction between pairs of slots.

A variation of the antenna system according to the invention is shown inFig. 4 wherein two conductive surface elements 32 and 33 ofsemi-circular cross-section are arranged to form a substantially tubularstructure having two continuous slots 24 and 25 therebetween. In thisinstance the transmission line conductors 28, 29 are transposed everyhalf wavelength at the operating frequency in order to maintain theedges of the slots in the proper polarity. A cross-section takentransversely through the structure of Fig. '4 will be the same as thatshown in Fig. 2, and the same explanation of the mode of operation willhold except for the transposition point at which lit tle or no radiationwill take place anyhow.

The effect of additional slots on the antenna system of the invention asthus far described can be seen by referring to Fig. 5. The cylindercontains four slots 24, 25, 42 and 43 spaced ninety degrees apart.Ttransmission line conductors 38 and 39 induce currents in thecontiguous wall portions 44 and 45 which follow the rules hereinbeforeset forth. The interposed wall portions 46 and 47, however, are neutralin effect and the whole radiation transferring element acts as thoughthe slots 24, 25, 42 and 43 are in series respectively.

A more versatile embodiment of the invention is shown in Figs. 6 and 7.A length of radiation transferring element has two groups of four slotseach, for example the slots 61-64, spaced about the periphery and twobalanced transmission lines comprising the conductors 38, 39 and 48, 49respectively arranged within the tubular element 50 for energizing theslots. The corresponding slots of each group are spaced apart by awavelength, or a multiple thereof, at the operating frequency. The slotsof each group may be on the same level, but preferably alternate slotsof each group are staggered by half a wavelength as shown in Fig. 6. Thecrosssection taken along the line 7-7 of Fig. 6 shows the slots in Fig.7 in the same manner as though they were on the same level for clarityof explanation and also to show that such a structure is feasible,although not the preferred embodiment.

One conductor 38 of one transmission line induces currents of equalintensity in the contiguous wall portions 54 and 51 which places theapposing edges of the adjacent slot 61 at the same instantaneouspotential and the other conductor 39 induces currents of oppositepolarity in both of the contiguous wall portions 55 and 56 which placethe apposing edges of the adjacent slot 62 at the same instantaneouspotential. Thus the slots 61 and 62 adjacent the conductors 38 and 39respectively of the one transmission line do not radiate any energytravelling down this transmission line. For this reason staggering ofthe slots is to be preferred in order to provide solid wallportions-which is above the slots 61 and 62 in the view of Fig.6-contiguous to the conductors for more eflicient transfer of energy. Ofcourse another reason for staggering the slots is to minimize the effectof any disturbing influence outside the cylinder 50 on the conductorswithin the area of maximum energy transfer to the wall portions. Theenergy travelling down the transmission line comprising the conductors38 and 39 is radiated by the other posite edges of the slots 63 and 64are of instantaneous opposing polarity. That is, the opposing edges ofthe radiating slots 63 and 64 nearest the one transmission lineconductor 38 will be of the same instantaneous polarity in response tocurrents induced by the conductor 38 in the contiguous wall portions 54and 57, while the apposing edges of each of the radiating slots will beof the opposite instantaneous polarity in response to energization bythe other transmission line conductor of the other wall portions 55 and56. Likewise, the conductors 48 and 49 of the other transmission lineenergize the slots 61 and 62 located in a plane and right angles to theplane defined by the conductors 48, 49 and have no effect on the slots63, 64 lying in the same plane. Thus there is pair of slots 63, 64because ap-,

escapes The two pairs of transmission line'con'ductors 38, 39 and 48, 49are preferably equidistantly located from'the center ,of the tubularmember 50in order to prevent any interaction therebetween. It is not anabsolute necessity, however, that the conductors all be spaced the samedistance from the center. It will besufiicient if the median planes" ofthe transmission line conductors interact at the center. The medianplane is defined as the plane normal to the plane defined by theconductors and passing through a point midway between them. Hence thetransmission line conductors may be considered to lie at the corners ofa rhombus, preferably a right rhombus or square, whereby interaction isavoided. Energy of phase quadra'ture relationship in the twotransmission lines will effect turnstilc radiation providing anomnidirectional field pattern of contra-rotating phase vectors such asis usedin the better television broadcasting installations today. Otherapplications of the structure will be immediately suggested to thoseskilled in the art.

Another embodiment of the invention is shown in crosssection in Fig. 8,wherein the conductors 38, 39 and 48, 49 are positioned to be near thecenters of the wall portions separating the slots 6164. The twotransmission lines each energize the four slots as explained inconnection with the structure shown in Fig. 5. This embodiment was builtand successfully operated at frequencies in the band 800-900megacycles-with the following dimensions, all in inches:

Curves 80 and 81 representative of the field pattern obtained byexcitation by means of the transmission line conductors 48 and 49 aloneare superimposed on the cross section. These'curves'are nearly perfectcircles. Similar curves wereobtained by energizing the slots by means ofthe transmission line conductors 38, 39 in phase quadrature and theresultant pattern was substantially perfectly circular. In thisdetermination the antenna was excited as a transmitting antenna butit'must be understood that inverse operation as a receiving antenna willbe equally efi'icient. The arrangements described in connection with thedescription of- Figs; -8 can be modified along the lines suggested inconnection with the" arrangement shown iri- Fig. 4. With two balancedtransmission lines it is necessary that the transposition of one line bemade substantially midway between the transposition of the other line;which is in effect equivalent to staggering of the slots as shown inFig. 6. The four continuously extending slots will efiect a verticalarray of better directivity than that afforded by antenna of equalheight according to the arrangement of Fig. 6 but due to some losses atthe transposition points the efficiency probably is not as great ascould be obtained with an antenna according to Fig. 6 of twice theheight. Cost and other factors will determine the ultimate constructionfor each case at hand.

It is also suggested that in accordance with the invention the elongatedslots may also be skewed with respect to the axis of the hollow tubularconductive member, in which case elliptical or circularly polarizedwaves result. The antenna of the invention may be prevented from icingand the like by blowing hot air up the tubular members 20 or 50 by aheater-blower combination (not shown) located at the base. For highpower and high temperature operation of the slotted cylinder antenna,cooling air may be blown into the tubular member.

Since the length of the conductive cylinder 20 or 50 may be from 20 tomore than 40 feet for ultrahigh frequency television broadcastingservice depending upon the gain required, it is desirable to employseveral sets of centering spacers. Three or four such spacers may beused at each of several layers along the length of the outer conductivecylinder to maintain the energy distribution between the transmissionline formed by conductors 38, 39 and 48, 49 in perfectly neutralrelationship. Each spacer is made of insulating material. It has beenfound that a polytetrafluorethylene material marketed under the tradename Teflon has highly desirable mechanical properties which combine ahigh insulation resistance, low dielectric loss, and low frictioncoefficient. Holes are provided in each spacer to allow moisturecondensation to drain and also for passage of heating and cooling air,if desired.

The invention claimed is:

1. An antenna system including a tubular conductive member havingelongated apertures disposed in opposing wall portions thereof and atwo-conductor open-type transmission line arranged within said tubularconductive memher, said tubular conductive member and said conductorsbeing located with respect to each other so as to couple energy betweensaid transmission line and said apertures by inducing currents in saidwall portions of said tubular conductive member.

2. An antenna system including at least two elongated conductive membersarranged and spacedapart to form a tubular structure having a pair ofoppositely disposed elongated apertures between said members, twoelongated conductors arranged Within said tubular structure and spacedapart from each other and from said conductive members at distances atwhich high frequency energy translated by currents in said conductors iscoupled through said conductive members and radiated in ambient space byway of said elongated apertures.

3. An antenna system including an elongated hollow conductive memberhaving at least two pairs of slots therein, the slots of each pair beinglongitudinally arranged in said member on substantially opposite sidesthereof, a pair of elongated conductors arranged within said conductivemember elfecting'an open-wire transmission line, a further pair ofconductors arranged within said hollow conductor to form anotheropen-wire transmission line, the'median planes defined by the first saidand said further pairs of conductors intersecting at the axis of saidhollow conductive member, and means to couple transducer apparatusacross said open-Wire transmission lines.

4. An antenna system including an elongated hollow conductive memberhaving at least two slots therein, said slots being longitudinallyarranged in said member and in opposing portions thereof, a pair ofconductors arranged within said conductive member and spaced apart toeffect an open-wire transmission line, said slots being coupled to saidtransmission line by currents induced in said conductive member, andmeans to couple transducer apparatus across said transmission line.

5. A slot antenna comprising a hollow tubular conductive member having aplurality of elongated slots therei in, each of said slots having alength of substantially a half wavelength at the operating frequency,said plu- I rality of slots being arranged in layers having acenterto-center spacing of a multiple including unity of one wavelengthat said frequency from the next adjacent layer, elongated conductorsdisposed within said conductive tubular member and capacitively coupledto said tubular member at the walls thereof, each slot being coupled toa pair of said elongated conductors solely by means of currents inducedin the Walls of said tubular conductivemember.

'6. An antenna system including a radiation transferring elementcomprising a tubular conductive member having a plurality oflongitudinally arranged elongated slots therein, a pair of conductorsrunning longitudinally Within said tubular conductive member and spacedapart to form a balanced transmission line, said conductors beingfurther spaced from the inner walls of said tubular conductive member torender the sole coupling between: said slots and said transmission lineby transfer of energybetween said transmission line and said tubularconductive member.

7. An antenna system comprising a plurality of conductive surfaceelements arranged to form a substantially tubular structure having atleast two elongated apertures between said elements, at least twoconductors arranged within said tubular structure and spaced apart toeffect a balanced transmission line, said conductors being free ofconnection to said conductive surface elements and spaced therefrom at adistance at which currents are induced therein to transfer highfrequency radiation to and from ambient space.

8. An antenna system including a tubular conductive member having aplurality of elongated apertures arranged in wall portions thereof, saidapertures being arranged in pairs with the slots of each pair located inopposing wall portions of said conductive member, a pair of-elongatedconductors arranged Within said conductive member, each of saidconductors being located adjacent a wall portion of said conductivemember to induce currents therein in response to potentials. appliedbetween said elon ated conductors, the currents induced by each of saidelongated conductors producing potential differences transversely ofsaid slots, thereby causing a transfer of energy between said elongatedconductors and ambient space.

9. An antenna system including at least one balanced conductortransmission line, a plurality of conductive surface elemental portionsarranged about and spaced from the conductors of said transmission lineto enclose the same except for a number of apertures between saidelemental surface portions, the spacing between said conductors and thedimensions thereof having values at which wave energy of the desiredoperating frequency is translated thereby, and the dimensions of saidconductors and the spacing of the conductive surface portions therefrombeing of values at which currents are induced in said portions and saidWave energy is translated through said apertures between saidtransmission line and ambient space.

10. An antenna system as defined in claim 9 and wherein the distancethat currents induced in said conductive surface elements travel inopposite directions is an odd multiple including unity of a halfwavelength at the operating frequency.

-. 11. An antenna system as defined in claim 9 and wherein the ratiobetween the diameter of a conductor and the spacing between thatconductor and the contiguous conductive surface element lies between0.15 and 0.20.

12. An antenna system as defined in claim 9 and wherein the ratio of thediameter of a conductor squared to-the product of the spacing betweenthat'conductor and'the conductive surface element and the radius ofcurvature in said conductive surface elemental portions define con-'-tinuous apertures :and the conductors of said transmis-' sion line aretransposed every half-wavelength at the op-j crating frequency toenergize each edge of said apertures in the same instantaneous polaritythroughout the entire length thereof.

14. An antenna system as defined in claim 9 and wherein there are atleast, four conductive surface elemental portions and there are twoapertures on either side of the plane defined by the conductors of saidtransmissio line.

15. An antenna system as defined in claim 9 and wherein the capacitivereactance between the transmission line conductors is substantiallyresonated by the inductive reactance of the conductive surface portionscarrying the induced currents to the edges of the apertures formedbetween said portions.

16. An antenna system as defined in claim 9 and where in there are atleast four conductive surface elements and each conductor of saidtransmission line induces substantially equal currents into two of saidportions at the same instantaneous polarity. I

17. An antenna system as defined in claim l6-and wherein the apertureremote from the transmission line conductors actas inductance elementsin series with the capacitive reactance between the transmission lineconductors and said conductive surface portions substanfrequency.

18. An antenna system as defined in claim 9 and wherein each of saidapertures is of substantially a half wavelength and alternate aperturesare in different levels.

19. An antenna system as defined in claim 16 and including a furtherbalanced transmission line having the conductors thereof located in themedian plane of the first said transmission line and equidistant fromthe conductors thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,408,435

Mason Oct. 1, 1946 2,658,143 Fiet et al. Nov. 3, 1953 2,665,381

Smith et a1. Jan. 5,-1954 tially to resonate said system-at the desiredoperating

